For so-called “blind applications”, i.e. for applications in which the installation point can only be accessed from one side, such as large metal sheets, special section tubes, bodywork parts or similar sheet metal parts, so-called “blind rivet nuts” have hitherto been used to introduce a nut thread into parts of this type. These blind rivet nuts (also denoted by BRN) are seated using a specific processing tool, in that by squeezing the blind rivet nuts, a so-called “closing head” is produced which fixes the nut. Since the corresponding blind rivet nuts per se and particularly also the closing head which has formed are relatively weak, in the past it has only been possible to use blind rivet nuts to attach light or ancillary components. The “high-strength blind rivet nut” developed by the company Avdel was the first blind rivet nut to also allow structural connections having relatively high pre-tensioning forces, due to the relatively high thread strength of said nut.
Even in the case of these high-strength blind rivet nuts, the problem arose relatively quickly that bolts with a strength of 10.9 or above, which are to be screwed as far as the yield point, generate such high pre-tensioning forces that the closing head starts to sink or starts to deform during the bolt installation. In the worst case, this would result in the closing head shearing off, i.e. the blind rivet nut would be destroyed and would then have to be replaced. In any case, the subsequent sinking/deformation would result in a significantly lower pre-tensioning force, compared to the presets given by the defined torque and angle of rotation bolting procedure. The additional angle of rotation caused a sinking/deformation of the BRN instead of the desired increase in pre-tensioning force. Due to this sinking or deformation, the industry routinely experiences problems in achieving the defined bolting curves even with high-strength blind rivet nuts and thus in monitoring the correct assembly of tie bars on vehicles, for example.
Another possibility known from the prior art of providing sheet metal parts with internal threads is the use of so-called cage nuts. However, to install cage nuts, in the prior art it was necessary for either the rear side of the part to also be accessible or additional auxiliary holes were required to introduce the cage nut from the side, as is necessary for so-called “C-clips” of the prior art. A cage nut of this type, configured as a clip, is disclosed, for example in EP 703 021 B1 which would appear to be the closest prior art in respect of the present invention.